Adjustable support legs of upper part of highland gap sprayer carry the chassis frame, the engine, transmission, chemicals liquid box and spray system, cab and other components, and the lower installs hydraulic motors, tires and other drive running system, that is a key component of highland gap sprayer to achieve adjustable height and track width. Through building the three dimensional (3D) digital prototype model of highland gap sprayer adjustable support leg, using the finite element method (FEM) to calculate the structural strength of the lower support legs of key bearing components in different conditions location, and according to the calculation result, the weak parts were improved in design. The results show that the structural design is rational, which provides a theoretical basis and data support for the final shape and structure parameter validation, and will be applied and verified in the prototype trial production and field tests.